1. Field of the Invention
The present invention relates to a stage position measuring apparatus, and more particularly to a stage position measuring apparatus provided in a projection exposure apparatus for use in manufacturing integrated circuits, liquid crystal bases, thin film magnet heads and the like, and for measuring by means of an optical distance measuring apparatus a position of a stage moving in one or two dimensions and on which a mask or a photosensitive substrate is provided.
2. Related Background Art
In a conventional stage position measuring apparatus, a stage moving in one or two dimensions is mounted within a chamber, and a position of the stage is measured by means of an optical distance measuring apparatus such as a laser interferometer.
The interior of the chamber is air-conditioned in its entirety, and an optical path for the interferometer is locally air-conditioned. More specifically, a local air-conditioning device supplies air to the interferometer optical path through a duct member. The temperature of the air supplied by the local air-conditioning device is identical to the temperature of air supplied by a general air-conditioning device.
In the conventional stage position measuring apparatus as mentioned above, however, an air temperature in the interferometer optical path is different from that of an atmosphere around the interferometer optical path to a certain degree. Such a temperature difference is caused by an offset generated by the influence of a heat generating source such as a stage and the like or by an offset between a controlled overall air-conditioning temperature at which the general air-conditioning device aims and an actual temperature of the atmosphere around the interferometer optical path. The temperature difference is also caused by an offset generated by the influence of heat transmitted from the duct and the like or by an offset between a controlled local air-conditioning temperature at which the local air-conditioning device aims and a temperature of air actually supplied from an air supplying opening for local air-conditioning.
Thus, mixed around the interferometer optical path are the two fluids having the different temperatures or the atmosphere around the interferometer optical path and the air supplied to the interferometer optical path from the air supplying opening for local air-conditioning. Therefore the conventional stage position measuring apparatus has a drawback in that a temperature fluctuation is generated at a value measured by the interferometer due to the mixture of the two fluids having the different temperatures.